This Planet Has One of the Weirdest Orbits We've Ever Seen

Exoplanet HD 20782b holds a fun new distinction. It's got the most eccentric orbit ever seen body of its type.

While the planets in our solar system (non-dwarf variety, at least) have a roughly circular orbit, the Jupiter-sized HD 20782b has an orbit around its sun that is so eccentric that it comes within scorching distance of its parent star before catapulting back out to 2.5 astronomical units away. To put that in layman's terms, that means that if it were in our solar system, it would go much closer to the sun than Mercury, and then all the way out to the asteroid belt.

That close approach gives astronomers a unique opportunity. The starlight of the alien sun reflects off the gasses in the upper atmosphere of the eccentric giant, allowing an opportunity to study its composition as well as the interaction with its parent star.

The unusual orbit is likely the result of an ancient collision with another planet that knocked HD 20782b into an eccentric orbit and knocked the other planet out of the solar system entirely. Alternately, a nearby binary star could have caused the orbit early in the system's migration before establishing its current orbital perch.

The research by San Francisco State professor Stephen Kane and colleagues was published in The Astrophysical Journal. A pre-print is available here.

A graphic illustrating the orbit of HD 20782b, a planet with an extremely eccentric orbit. To give a sense of orbital scale, it's been superimposed over our solar system.

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